1. Field of the Invention
The present invention relates to catheter assemblies and more particularly concerns a catheter having active fluid control valve features.
2. Description of Related Information
Various procedures such as a method of intravenous therapy known as hyperalimentation and certain regimens involving chemotherapeutic drugs require the use of a catheter which may remain in the patient's body for a period of days, weeks or even months. A typical procedure involves inserting the catheter through the subclavian vein, located near the collar bone, and advancing the catheter to the superior vena cava, an area of substantial blood flow of the heart. In some long term catheterization procedures the physician may reroute the exposed end of the catheter from the original entry, near the collar bone, subcutaneously through the patient's body and out in the abdominal area so that the patient can, in some cases, resume many normal activities without having a catheter protruding from his collar bone area.
These catheterization procedures are routinely performed with a conventional catheter having an open distal end. Blood flow out of the body is prevented by occluding a portion of the catheter which is external to the patient's body. In many instances, the portion of the catheter outside of the body is covered by an injection cap which includes a pierceable septum to allow injection and withdrawal of fluids through the septum. This type of catheter has disadvantages in that the open end of the catheter, which is positioned in the patient's body provides an area for the formation of blood clots. The potential for formation of clots is undesirable because clots can occlude the catheter and prevent therapy or a clot can separate from the catheter and travel to other areas of the vascular system and possibly cause injury by occluding a vessel. The type of catheter, having an open distal end, must be frequently flushed with a heparinized saline solution to clean the catheter area and reduce the potential for clot formation. This periodic maintenance, in itself, provides a potential for irritation by manipulation of the catheter and introduces an anticoagulant (heparin) into the blood stream which may affect the patient and/or blood test results. In addition, if the external cap is inadvertently removed, there is the danger of introducing an air embolus into a vein and potentially injuring the patient. Further, the blunt open end of the catheter interferes with blood flow and is believed to cause turbulent eddies in the area of the tip which may also promote clot formation.
Many of the above-recited problems could be eliminated if the central venous catheter were provided with a closed distal end portion. However, some type of port or valve means must then be provided. Schulte, in U.S. Pat. No. 3,111,125, teaches a ventriculo-atrial shunt apparatus comprising an inlet tube for placement in the cranial cavity, a manually operatable lamp subcutaneously implanted on the skull and an outlet tube extending between the pump and the atrium portion of the heart. Schulte's outlet tube has the desirable closed distal end and a plurality of slits around the periphery of the distal end of the tube acting as slit valves. Schulte teaches that fluid pressure in the tube will force the slits open so that fluid will flow freely when a sufficient pressure differential exists between the fluid within the tube and the area outside the tube.
Along these lines Groshong et al. (U.S. Pat. No. 4,559,046) teach a catheter device for intravenous therapy having a flexible closed distal end including a slit-type valve as described in Schulte and further including a twisted wire removable stiffener which can be used to facilitate insertion of the catheter into the patient and then removed. The distal end of the stiffener abuts against the interior closed end of the catheter when the stiffener is used to push the catheter through the vein. The stiffener does not occlude the catheter lumen.
It is desirable that a valve means in a central venous catheter should allow fluid flow through the catheter and into the patient, and fluid flow from the patient's vascular system out of the catheter which is desirable, for example, when obtaining a blood sample. Slit valves present a problem because inwardly directed pressure may tend, under some conditions, to shut the slit valve more tightly rather than to open it. Groshong et al., in U.S. Pat. No. 4,549,879, teach an improvement to make the slit valve more useful with respect to fluid flowing therethrough into the catheter. Groshong et al. teach that the use of stiff thermoplastic material in catheters has disadvantages in that the slit can cause damage to cellular elements which are injected into the body or withdrawn from the body through the slit. Groshong et al. teach the use of soft materials such as silicone rubber made in a thin cross-section and treated with dimethylsiloxane for weakening and making the catheter wall more pliable in order to facilitate the two-way valve function.
The closed end catheters having slit-type valves overcome many of the deficiencies of the open end catheter as recited hereinabove. The closed end catheters having slit-type valves as taught by Schulte and Groshong et al. still have deficiencies. Most notably the slit-type valve is more adaptable to situations where outward flow is desirable and inward flow is not desirable because of its directional properties. Groshong et al. teach how to partially overcome this problem by making the catheter of soft material and weakening the structure around the valve so that it opens under a pressure differential in either direction. However, even the improved valves taught by Groshong et al. require a pressure differential for opening in either direction and therefore are not readily usable for certain tests involving pressure measurement using a transducer in the catheter assembly, such as measuring the central venous pressure, because the proximal open end of the catheter is not in free fluid communication with the vascular system. Also, it is still believed that the slit-type valve can cause damage to cellular elements passing through the valve because of the forces required to open the valve. Cells needed for blood testing may be damaged and cells being introduced into the vascular system may also be damaged. Further, as the distal end of the catheter is made of softer material and treated to be weaker and weaker in order to attempt to overcome the deficiencies of the pressure activated slit-valve, the tip of the catheter becomes weaker. This weakened tip is more prone to bending caused by patient movement or muscular movement within the patient's body, and the tip may be bent in such a manner as to open the valve in the absence of a fluid pressure differential across the valve. Accordingly, there is a tradeoff between optimizing the valve performance so that the valve is responsive to fluid pressure differentials between the inside and the outside of the catheter, and providing a valve that stays shut during normal use conditions.
Catheters having closed distal ends and passive valve means have been addressed by the prior art, as alluded to above. However, there is still a need for a simple, straightforward, reliable, easily fabricated catheter having a closed distal end and active valve means which will minimize the potential for damage to cellular elements in liquid passing through the valve means and also minimize the potential for inadvertent opening of the valve which can result in patient blood loss or introduction of an air embolus into the patient's vascular system. It is also desirable to have a catheter assembly which will readily allow blood pressure determination using transducer devices connected to the catheter assembly.